Update: ...and if I'd learn to read the entire thread before posting, I'd've seen that you already thought of a better hack, and zentara already provided a nice starting point to a nice way to do it. IGNORE THIS POST!

* UGLY HACK ALERT * If you're offended by hacks, STOP READING NOW!

I'm no UI guy, so I would cheat with a hack: Instead of making a grid of labels (I assume you're just changing their color to draw the spectrum?), you could make a simple linear array off 100 of them, and simply change their heights. This will let you get the job done with fewer labels, and fewer operations (rather than update 4000 labels, you need only update 100), so you could get a better repetition rate.

...roboticus